Prior to the advent of computer networks, problems were solved primarily by the brute force of a single processor that churned away until solution, error, or timeout. This early paradigm of computing envisioned that users would voluntarily queue up for stationary computing resources and wait patiently until their processing requests were serviced.
The introduction of computer networks and personal computing forever changed user expectations of what computer systems can accomplish. Individual users would no longer expect to travel to a particular location to have their processing needs met. Instead, individuals would expect that sufficient computing power would be sitting on their desk to get the job done; or, at least, that their personal computers would be networked to sufficient resources remote from their location.
Early forms of personal computing, however, limited the usefulness of this paradigm. One problem was that early personal computers were virtually immovable boxes sitting on individual desks. The static nature of personal computers confined users to one location, focusing their attention upon the box which embodied the computer. This limitation did not allow for a full range of human user interactions. For example, personal computers do not adequately support spontaneous, face-to-face meetings between several people that may occur at various locations throughout the workplace. Although the advent of "portable" personal computers, such as laptops or notebooks, helps facilitate these meetings, several people must still huddle around a common screen display to work collaboratively.
Other attempts were made to improve these personal computers by increasing their "user-friendliness". Windows were developed to give users the illusion of working from one's desktop. This metaphor suffered, however, from the size limitation of the monitor screen available to most personal computers--no one would ever think of using an actual desktop only nine inches high by eleven inches wide. Again, personal computers were static objects commanding the attention of users.
An alternative paradigm to personal computing considers integrating computers, of varying size and power, in large numbers into a typical office environment. The integration of these computers could be achieved "ubiquitously" in such a way that the inhabitants of such an environment would not notice the existence of these computers. In his article, "The Computer for the 21st Century", (Scientific American, September 1991 issue), Dr. Mark Weiser describes a "ubiquitous computing" work place in which there would be literally hundreds of computers per room. These computers would provide a level of functionality that no single personal computer provides today.
In Weiser's work space, this integration forms a hierarchy in terms of size and performance. At the lowest end, "tabs", typically only a few inches square, are the smallest components of ubiquitous computing. Tabs would perform basic functions in a ubiquitous setting. For example, tabs have been used as "active badges" that are worn by people inhabiting this environment. As a wearer of this badge walks from room to room, the badge would communicate to the room, through a wireless medium, the presence of the wearer. Automatically, the room might make adjustments for the individual, such as dimming lights, adjusting room temperature, and the like. Additionally, the building itself could keep account of an individual's movements. Phone calls could be forwarded to the room where the individual is located. Likewise, security doors would open up for a certain individuals and not for others.
At the other end of the hierarchy, "pads" and "boards" are computers analogous to sheets of paper and blackboards respectively. These computers, together with tabs, work interactively with each other to form a seamless web of computing in the work place. Ideally, in any given room, hundreds of tabs may work and communicate with ten or twenty pads and one or two boards.
Tabs that have an active display, as well as pads and boards, may serve to augment the amount of display available to exhibit data. As described in Dr. Weiser's article, a user may be able to migrate any window that may appear on a workstation screen onto a tab, pad or board. The advantages of migrating windows onto tabs, pads or boards are usability and portability. Transporting a window flees up additional space on a screen for other information. Additionally, transported windows on several tabs or pads could be spread across an actual desk top--exactly as people would spread a set of working papers. Carrying a project to another room would be as simple as collecting all the relevant tabs and pads and physically walking.
Although there may be several ways to support a "ubiquitous computing" environment to accommodate the entire range of mobility required for these ubiquitous computers, the preferred implementation is a network that allows "wireless" communication with mobile devices. To date, many "wireless" networks have already been designed--the most notable, perhaps, being the cellular telephone network.
The "area" of a network employing the present invention may vary according to the needs and goals of the intended users. In the context of an office setting, a "local area" network is likely to be sufficient to use as a backbone. It will be appreciated, however, that the principles of the present invention may find application in networks of varying areas.
Some wireless networks have already been designed for the office place. For example, in U.S. Pat. No. 5,210,753 issued to Natarajan on May 11, 1993, entitled "Robust Scheduling Mechanism for Efficient Band-Width Usage in Multicell Wireless Local Networks", Natarajan discloses a method for partitioning transceiver nodes into maximally independent sets of non-interfering nodes for efficient scheduling of transmission.
In U.S. Pat. No. 5,212,806, issued to Natarajan on May 18, 1993, entitled "Distributed Control Methods for Management of Migrating Data Stations in a Wireless Communications Network", Natarajan discloses a method of handing off communication ownership of mobile units as they cross node/cell boundaries.
These above-mentioned patents are generally concerned with the physical layer of the network and, more specifically, with methods of transferring the communication links of a mobile unit from one base station to another. These issues might be better classified as problems in "communication continuity". Communication continuity is concerned primarily with mechanisms for providing a continuous pathway for data between two or more units, at least one such unit being mobile; and once disrupted, how to reestablish a data pathway.
By contrast, "processing continuity" is defined by the goal of maintaining a current and proper processing context between two units. Processing continuity ensures that either potential intermediate results are delivered to the end-user in a timely fashion or that these intermediate results are not generated (e.g. "blocked").
None of the above-mentioned patents disclose a mechanism for providing processing continuity between a mobile unit and a remote host. One of the features of the ubiquitous computing environment is that the mobile unit is ideally small and portable. This feature may necessitate minimal power consumption by the mobile unit and, hence, limited processing capabilities. Thus, a ubiquitous computing unit, such as the tab, may only require a small processor and limited memory sufficient to support communication with distributed applications. To achieve this type of mobile, distributed processing, the network must have sufficient mechanisms to provide not only communication continuity but also processing continuity.
These higher level issues are discussed in another article by Dr. Mark Weiser, entitled "Some Computer Science Issues in Ubiquitous Computing" published in the July 1993 issue of Communications of the ACM. One of the problems identified by Dr. Weiser is the dynamic location updating required when mobile units roam from base station to base station. A number of solutions proposed to this problem involve an additional layer of network addresses. This additional layer may be embodied in the implementation of special routing nodes. Special routing nodes would keep track of the real address of the mobile unit and forward packets addresses to the unit appropriately.
One design issue that arises is whether location information should be centralized or distributed. There are many reasons for selecting one design over the other, such as ease of implementation and system performance. For example, while a centralized database of location information may be easier to implement and manage as a system resource, a centralized database may become a bottleneck degrading system performance. Additionally, other reasons exists, including social ones--the choice between a centralized and a decentralized database may depend on the level of security and privacy desired by the system users.
These design choices have been made in a number of current systems. For example, in U.S. Pat. No. 5,159,592 issued to Perkins on Oct. 27, 1992 and entitled "Network Address Management for a Wired Network Supporting Wireless Communication to a Plurality of Mobile Users", Perkins discloses the use of a global gateway to properly route packets from remote hosts to mobile units. The global gateway maintains a list of "pseudo-addresses" that are used by remote hosts to address mobile units. The global gateway, in turn, relays the packet to the local gateway that is currently managing the mobile unit. If the mobile unit is turned off, the remote host's message is buffered by the global gateway until the unit returns to service. Once in service, the buffered packets are then forwarded to the mobile units.
Likewise, in U.S. Pat. No. 5,181,200, issued to Harrison on Jan. 19, 1993 entitled "Handoff Method and Apparatus for Mobile Wireless Workstation", Harrison describes a store-and-forward method whereby packets intended for a mobile unit that loses connection with the network are stored in a spooler until connection is re-established. Upon restoring connection, the spooled data packets are transmitted to the unit in a "first in--first out" fashion from the spooler. Both Perkins and Harrison employ centralized name services and some form of buffering to effect a measure of continuity in their respective systems.
A decentralized name service, however, may be desirable in a ubiquitous computing environment. In such an environment, mobile units may have several, associated application processes all vying for the attention of the unit. This is especially true for a user's tab which is being used as a Personal Digital Assistant (PDA). As a user roams around such an environment, a user may have access to a number of processes that control certain functions in the environment or that may be supplying the user with requested information. These processes may desire the attention of the user tab to inform the user of their status. As the mobile unit temporarily loses connection to the network, the accessible processes must preserve their status and information until such time that connection is re-established.
A global name service tasked with resolving all the references among these different processes to mobile units might become the bottleneck to reasonable system throughput. This is particularly true if the name service is also tasked with providing authorization access for all processes wishing to communicate with a mobile unit. Otherwise, if the name service allows unlimited access to mobile units, then individual users might lose a degree of security and privacy that is otherwise desirable.
Additionally, mechanisms, other than buffering, may be more advantageous for processing continuity. Buffering is inherently limited to the amount of storage allocated. Likewise, if several processes are attempting to communicate with the mobile unit simultaneously, a scheme to separate and reassemble the buffered packets from the various processes must be implemented.
Thus, there is a need for a mechanism that allows for easy updating of mobile unit locations and the preservation of processing status of communicating applications while, simultaneously, allowing users to control which processes have access to their units.
It is thus an object of the present invention to provide a mechanism that allows processing continuity to mobile units by preserving the status of accessible processes that desire communication with the unit.
It is also another object of the present invention to provide a mechanism for easy updating of a mobile unit's location to facilitate communication between units and their associated processes.
It is yet another object of the present invention to provide a mechanism to allow user discretion in which processes have access to their mobile units.